The invention relates to substrate carriers used to hold memory disks or wafer substrates during a polishing process, and to methods for manufacturing such carriers.
Hard disk drives contain aluminum disks of remarkable smoothness and flatness. Likewise, wafers used to make semiconductors also must have an exceptional surface finish. The aluminum disks and wafers (both referred to as xe2x80x9cdisksxe2x80x9d or xe2x80x9csubstratesxe2x80x9d in this disclosure) must be polished in order to obtain the desired level of smoothness . The preferred polishing process is commonly referred to as chemical-mechanical polishing or CMP.
In the CMP process one or more disks are placed in a consumable thin flat substrate carrier 10 shown in FIGS. 1 and 2. Carrier 10 includes four receptacles or pockets 11 for receiving disks. In the illustrated form of the invention, which is adapted for double sided polishing, each receptacle 11 extends all the way through the carrier material. Other carriers may be adapted for single sided polishing and include receptacles which do not extend all the way through the carrier material. Although four openings 11 are shown for purposes of example, carriers may have any number of disk receiving receptacles or pockets. The radius of the substrate carrier 10 ranges between approximately 3 and 16 inches. The thickness of the carriers 10 must be less than the substrate thickness and generally falls between 0.012 and 0.35 inches.
Disks (not shown) are inserted into the substrate carrier openings 11 and transported by the carrier through the polishing process. The substrate carrier 10 is driven through the process by pins or gears that turn and/or rotate the carrier 10, or perhaps many carriers, around a planetary gear or pin drive (not shown). The illustrated carrier 10 includes a peripheral gear 13 which allows the carrier to be driven through the polishing process.
Prior to the present invention, substrate carriers used during the polishing or grinding process have been made of metals, such as steel and aluminum, or of xe2x80x98continuousxe2x80x99 fiberglass filled epoxy. xe2x80x98Continuousxe2x80x99 means that the actual glass fibers 14 are over several inches in length as seen in FIG. 4. The original metal substrates were replaced by continuous glass mat reinforced thermoset epoxy composites called F4 or G10 as shown in FIG. 4. These epoxy/fiberglass carriers replaced the prior metal carriers in an effort to reduce the quantity of abrasives worn off the substrate carrier during the process. The fiberglass filled epoxy substrate carriers are made by typical thermoset composite lay-up techniques.
The standards for flatness and smoothness of wafers and memory disks continually increases in order to accommodate more information or chip architecture on the memory disks and wafers. As the standards for flatness and smoothness increase, rejection rates have also increased to as much as 40%, attributed to scratches from worn fiberglass particulates released from the epoxy/fiberglass substrate carrier. As the epoxy/fiberglass carriers wear away, the polymer layer over the fiberglass mat, the wear rate of fiberglass particulates increases. The current epoxy/fiberglass substrate carriers must be replaced at the first signs of wear to avoid rejection rates greater than 40%. A leading manufacturer of hard disks has indicated that scratches attributed to worn fiberglass particulates cause 15% on average of their disks to fail.
The prior art epoxy carriers must have the continuous glass reinforcement 14. These G10 or F4 epoxy carriers without glass materials are of insufficient strength to work as a substrate carrier. Epoxy typically has a tensile strength of less than 5000 psi in the neat form. Current substrate carriers are made with a woven fiberglass mat in the center to give the epoxy carrier higher strength and stiffness as in FIG. 4. Additionally, the fiberglass mat reinforcement of the epoxy carriers has anisotropic stiffness and strength due to the bi-directional orientation of the continuous glass fibers. Fiberglass/epoxy carriers are used in over 95% of the polishing processes for memory disks today.
It is an object of the invention to provide a substrate carrier which overcomes to above-described problems and others associated with prior substrate carrier used in substrate polishing operations. More particularly, it is an object of the invention to provide a substrate carrier which minimizes the release of particulates which may interfere with the polishing process. Another object of the invention is to provide a method for manufacturing such a substrate carrier.
These objects are accomplished by injection molding a substrate carrier from a plastic material. The plastic material may be either neat or contain non-abrasive reinforcing materials. Molding may comprise traditional injection molding or modified-injection molding in which the mold is maintained in a partially open position during at least part of the plastic injection step.
A substrate carrier according to the invention minimizes the release of materials which may interfere with the polishing operation. Particularly, the molded plastic substrate carriers of the present invention do not release abrasive particulates as the carriers are consumed in the polishing process. The present carriers thus minimize the occurrence of scratches in the substrates and minimize substrate rejection rates after the polishing process.
These and other objects, advantages, and features of the invention will be apparent from the following description of the preferred embodiments, considered along with the accompanying drawings.